Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants are chilling sensitive, and do not naturally accumulate glycinebetaine (GB), a metabolite that functions as a stress protectant. We reported previously that exogenous GB application enhanced chilling tolerance in tomato. To understand its protective role better, we have further evaluated various parameters associated with improved tolerance. Although its effect was most pronounced in younger plants, this benefit was diminished 1 week after GB application. When administered by foliar spray, GB was readily taken up and translocated to various organs, with the highest levels being measured in meristematic tissues, including the shoot apices and flower buds. In leaves, the majority of endogenous GB was found in the cytosol; only 0.6–22.0% of the total leaf GB was localized in chloroplasts. Immediately after GB application, levels of H₂O₂, catalase activity and expression of the catalase gene (CAT1) were all higher in GB-treated than in control plants. One day after exposure to chilling stress, the treated plants had significantly greater catalase activity and CAT1 expression, although their H₂O₂ levels remained unchanged. During the following 2 d of this chilling treatment, GB-treated plants maintained lower H₂O₂ levels but had higher catalase activity than the controls. These results suggest that, in addition to protecting macromolecules and membranes directly, GB-enhanced chilling tolerance may involve the induction of H₂O₂-mediated antioxidant mechanisms, e.g. enhanced catalase expression and catalase activity.

Plantaricin W (Plw) is a new two-peptide bacteriocin, from Lactobacillus plantarum, which inhibits a large number of Gram-positive bacteria. The two peptides, Plwα (comprising 29 residues) and Plwβ (comprising 32 residues), were isolated from the culture supernatants and characterized. The individual peptides had low antimicrobial activity but acted synergistically, and synergism was seen at all mixing ratios tested. The data indicate that the two peptides work in a 1:1 ratio. Chemical analyses showed that both peptides are lantibiotics, but two unmodified cysteines and one serine residue were present in Plwα, and Plwβ contained one cysteine residue. The Plw structural genes were sequenced and shown to encode prepeptides with sequence similarities to two other two-peptide lantibiotics, namely staphylococcin C55 and lacticin 3147. The conserved residues are mainly serines, threonines and cysteines that can be involved in intramolecular thioether bond formation in the C-terminal parts of the molecules. This indicates that these bacteriocins are members of a new family of lantibiotics with common bridging patterns, and that the ring structures play an important functional role. Based on the data a structural model is presented in which each peptide has a central lanthionine and two overlapping thioether bridges close to their C-termini.

Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants were transformed with a gene for choline oxidase (codA) from Arthrobacter globiformis. The gene product (CODA) was targeted to the chloroplasts (Chl–codA), cytosol (Cyt–codA) or both compartments simultaneously (ChlCyt–codA). These three transgenic plant types accumulated different amounts and proportions of glycinebetaine (GB) in their chloroplasts and cytosol. Targeting CODA to either the cytosol or both compartments simultaneously increased total GB content by five‐ to sixfold over that measured from the chloroplast targeted lines. Accumulation of GB in codA transgenic plants was tissue dependent, with the highest levels being recorded in reproductive organs. Despite accumulating, the lowest amounts of GB, Chl–codA plants exhibited equal or higher degrees of enhanced tolerance to various abiotic stresses. This suggests that chloroplastic GB is more effective than cytosolic GB in protecting plant cells against chilling, high salt and oxidative stresses. Chloroplastic GB levels were positively correlated with the degree of oxidative stress tolerance conferred, whereas cytosolic GB showed no such a correlation. Thus, an increase in total GB content does not necessarily lead to enhanced stress tolerance, but additional accumulation of chloroplastic GB is likely to further raise the level of stress tolerance beyond what we have observed.

Solanum commersonii and Solanum tuberosum are closely related plant species that differ in their abilities to cold acclimate; whereas S. commersonii increases in freezing tolerance in response to low temperature, S. tuberosum does not. In Arabidopsis thaliana, cold-regulated genes have been shown to contribute to freezing tolerance, including those that comprise the CBF regulon, genes that are controlled by the CBF transcription factors. The low temperature transcriptomes and CBF regulons of S. commersonii and S. tuberosum were therefore compared to determine whether there might be differences that contribute to their differences in ability to cold acclimate. The results indicated that both plants alter gene expression in response to low temperature to similar degrees with similar kinetics and that both plants have CBF regulons composed of hundreds of genes. However, there were considerable differences in the sets of genes that comprised the low temperature transcriptomes and CBF regulons of the two species. Thus differences in cold regulatory programmes may contribute to the differences in freezing tolerance of these two species. However, 53 groups of putative orthologous genes that are cold-regulated in S. commersonii, S. tuberosum, and A. thaliana were identified. Given that the evolutionary distance between the two Solanum species and A. thaliana is 112–156 million years, it seems likely that these conserved cold-regulated genes—many of which encode transcription factors and proteins of unknown function—have fundamental roles in plant growth and development at low temperature.